Magnetic delay element



Feb. 2, 1960 Y slLVERMAN 2,923,834

MAGNETIC DELAY ELEMENT Filed D60. 28, 1956 FlG.l.

SIGNAL GENERAT GENERATOR INVENTORI BERNARD SILVERMAN BY I) E M qr'l ATTORNE United States Patent 2,923,834 MAGNETIC DELAY ELEMENT Bernard Silverman, Syracuse, N.Y., asslgnor to General Electric Company, a corporation of New York Application December 28, 1956, Serial No. 631,147

12 Claims. (Cl. 307-88) output pulses which may be added in series or employed individually to perform time dependent functions.

The employment of a single path magnetic saturable reactor as a timing or delay element is disclosed in a copending application, Ser. No. 631,167 of Benjamin G. Walker assigned to the assignee of the present invention and filed concurrently herewith. v

Delay elements find application in many arts, one of which is color television wherein it is necessary to provide delay for isolating the color burst from the rest of a received signal in order to eliminate components of substantially the same frequency as the color burst from the color burst amplifier. The color burst is located in the signal after the horizontal synchronizing pulse upon the pedestal carrying the horizontal synchronizing pulse and occurs during the blanking period or fiyback time of the horizontal sweep. Previously, in order to isolate the color burst from the remainder of the received signal, relatively complicated circuitry has been used in order to achieve the proper delay.

In other areas such as pulse communication systems, radar range gates and digital circuitry, it is also desirable to be able to derive a series of time coordinated output pulses from an input signal in order to perform time re lated functions. In involved circuits of this nature, reliability, space and weight problems are often serious. It is therefore an object of my invention to provide improved means to perform these functions and to reduce space and weight and greatly increase reliabilityin the circuitry employed.

Another object of my invention is to provide a multipath magnetic delay element which will provide a series of time related output pulses which may be either added or taken off individually as desired.

Still another object of my invention is to employ a magnetic delay element in order to achieve the abovementioned color burst delay.

A further object of my invention is to provide a versatile magnetic delay element which is highly reliable, small and light.

A still further object of my invention is to employ a magnetic delay element having multiple paths in order to achieve a desired gating pulse width and waveshape as well as a desired delay. I

Incarrying out my invntion in one form thereof, I employ a three-legged magnetic core having an inside leg positioned off center in order to provide two parallel magnetic paths having different lengths. Small air gaps are placed in all three legs. An input winding is wound on the inside leg and separate output windings are wound on each of the portions of the core'exterior to the inside leg. These output. windings are connected in series aiding. When an alternating input current, of willcient magnitude to saturate the paths in both directions,

tlows through the input winding, a delayed output pulse appears across the output windings. The total output voltage pulse represents the sum of the voltages induced in the output windings when each path is passing through the unsaturated region and appears a predetermined time after the change in polarity of the input current.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, together with furtherobjects and advantages thereof can best be understood by reference to the following description taken in connection with the accompanying drawing in which Fig. 1 is an illustration of one embodiment of my invention; Fig. 2 is a diagram illustrating the rela tionships between the various currents and voltages during the operation of the embodiment shown in Fig. 1; Fig. 3 is an illustration of hysteresis loops exhibited by theoretical and practical magnetic cores employed in my invention: Fig. 4 is a generalized embodiment of my invention; Fig. 5 illustrates an alternative embodiment of my invention employing different core structure.

Referring specifically now to the embodiment of Fig. 1, I have shown a core 10 preferably made from a magnetic material having a substatially rectangular hysteresis loop. Core 10 has three legs, two outer legs 11 and 1 and an inside leg 13. The inside leg 13 is placed off center as shown. An input winding N is wound on inside leg 13. The core 10 has two parallel magnetic paths or circuits including inside leg 13 as the common leg. A winding N is wound on and inductively coupled to the parallel magnetic path including the outside leg 11, externally to the inside leg 13. A winding N, is wound on the parallel magnetic path including the outside leg 12, externally to inside leg 13. The winding N; has two terminals 17 to which a signal generator 18 is connected. Winding N; has terminals 19 and 20 and winding N has terminals 21 and 22. Windings N, and N are connected in series aiding by connecting terminals 20 and 21. An output can then be taken from terminals 19 and 22. Alternatively, generator 18 can be connected to terminals 19 and 22 across the series combination of N and N and terminals 17 can serve as output terminals. In addition, the connection of terminals 20 and 21 may be used as a common terminal between windings N and N for a purpose which will be more fully explained hereinafter.

The operation of the above-described magnetic delay element of my invention may conveniently be understood by considering its use as a delay element to derive a gating pulse for a color burst amplifier in a color television receiver. When an alternating current input signal is applied by signal generator 18 to winding N, at terminals 17, the magnetic field intensity or magnetizing force is greater in the shorter magnetic path of core 10, that is in the magnetic path above-described including the outside leg 11, since the path length of this magnetic path is shorter and the number of ampere-turns passing through the input Winding N is equivalent in both magnetic paths. Due to the differences in magnetic field intensities, the times required to drive the two magnetic paths out of saturation after the reversal of the input current, or the delay times, will differ.

In Fig. 2a there is illustrated a television receiver input signal, the leading portion of which contains picture information 23. A pedestal 24 contains the horizontal synchronizing pulse 25 followed by a burst 26 of color synchronization information which it is desired to supply to a color burst amplifier (not shown). It is necessary to isolate the color burst 26 from the other portions of the input signal in order to eliminate harmonics of substantially the same frequency as the color burst from the amplifier; To do this the color burst amplifier is gated 7 horizontal sweep-"currentof Fig. 2b' is'suppliedto'termi- 1121s 17 01:- input *winding N of core 10 of :Fig. 1, the

magnitude being controlled so as to be sufiicie nt' 'to saturate both magnetic paths alternately in both directions. At time t in Fig. 2 the sweep current "passes through zero andchanges polarity. 1 Assuming that the magnetic path inclu'dingi'leg 11 has been'saturated in a negative direction. prior to -1 sufficient magnetic field intensity orxrnagnetizing'force will have'beenapplied thereto by time t to'drive this magnetic path-'out'of negativeisaturatio'n'and to cause a voltage to appear across the winding N ,.=as*is-illustrated'in Fig. 2c. 'Bytime t the magnetic path con'tai-ning the outside leg 11 is driven back into saturation in the-positive direction and the output'voltage across the winding N disappears. "However, at this time the path-"containingthe outside leg 12 has received sufiicient. magnetizing force to drive it out of negative saturation anda' voltage appears-across the winding N as is illustratedin'Fig. 211. At time't the path containing'the outside leg12- is driven back into positivesaturation and thewoltage across winding N "disappears. Since windiiigsfiNz and N5, are connected inseries aiding, a. composite output: voltage pulse isderived, as shown in Fig. 2a, which 1 constitutes the sum of the voltages across the" windings N andN between the times t and t .Attime t the polarity of the sweep currentof Fig.2b again changes and shortly thereafter, at time t the path containing the outside'leg lllis drivenout of positive saturation and a pulse appears across the windingN as is shown in Fig. 20. At time t this path-returns to nega- I tiversaturation'and the voltage across the winding N disappears. The 'path containing theoutside leg '12 is then "driven out of positive *saturation and avoltage appears across the winding N as is shown in Fig. 2d. At timet this path returns to negative saturation and the voltage disappears from the winding N 'As previing and later unscrambling signals. In digital circuitry "an input might be "integrated an'd'ad'ded or subtracted,

the position of the last output pulse yielding a digital representation of the input and also possibly performing an analogue to digital conversion. In digital applications a core having ten magnetic circuits could provide decimal representation.

The amount of delay achieved by this device is determined by the time :it-takes-to drivethecore-out of saturation after areversal in theinput current. Lhave illustrated in Fig. 13a an,ideal hysteresisiloop of a core having a rectangular loop. In this figure, H "illustrates the amount of magnetic afield intensity-or magnetizing force necessary to drive the corepoutof saturation when proceeding up the right-hand side of the'loop after the change in direction of input current. The magnetizing'force H is equal to a constant times the current or, more specifically, to a, constanttimes the.current,times,the number ouslygthese voltages across the windings N and'N are again added to achieve acomposite output voltage pulse, shown in Fig. 2e, between the times t and t pulse appearing across the combined'output during the time-t and t however, it is of greater'magnitude since the volt-time integrals of these two pulses are equal. This d'ifierenceinpulse height is caused by the greater slope ofthe sweep signal current of Fig. 2b during the fiyback time from t to t since the rate of change"of flux is dependenton the rate of change of currentin the input winding. The gating circuit of the color burst amplifier (not shown) requires a pulse of the polarity and order (if-magnitude of that shown between times t and min Fig. 2d to keep it gated on.

If it is desired to obtain individual time related output pulses instead of the sum as shownand described above for" puls'e-stretching purposes, individual pulses as illus-' trated in Figures 20 and 2d can be obtained by connecting arsuitable utilization device (not shown) to thefree terminalsf-19 and 22 with terminal 20 or terminal21'used as areference orcommon terminal. -Such a utilization device requiring separated pulses rather than a-composite 'pulse.couldiconsist of a radar range gate in which separate. time related pulsesare used to periodically'gate the portion of the'range visible ona radarscope through raw-series of outward steps. Another device could consist of a pulse communications system in which a series of pulses might be desired to indicate presence or absence or magnitude of an applied signal. Also in pulse communications a signal is often transmitted as a series of spaced pulses instead of a composite signal .in order to This composite pulse is of shorter duration than the composite of winding tumsdivided by thepathlength. Thus the delay may bec'hanged bjy hangingthe magnetizing force, which in turn maybechangedby altering the number of 't'urnsin" the inputfwinding'or by changing therespective pathlengths. y,

duc ng asaplint acorehaving a rectangular loop similar ,tothat shoiwnin Fig. 3,1 1, alters the loop in a manner illustrated, in'Fig. ,312. by increasing the slope of the loop. This tends to incre 'the;dhrationoftheoutput Pulse or th durat on .otthetlmethat .t ecore r mainsw f u t on. AlsoiHo and the. delayare. reduced. As an alternative, thejde'lay can bevcontrolled electrically by means of a bias current supplied'to one of the existing windings or to a's eparatebias winding on the core.'

.The amplitudeof the output signal of the embodh. ment of Fig. 1 may be varied by changing, thenumber of turns onthe windingsfN and N2. If his desired to provide equal output'volta'ges in ,each winding, each musthave a. different number of turns since the lengths ofthe' two magnetic paths are unequal.

The addition of" two pulses having'different delay times to'produce a composite delayed pulsehas ,beenfound necessary in. the above-describedburst gate application, sincethe time duration otthe' individual pulses may not belong. enough and since in practice the use of typical singleoutputpulsegtobetapered ina manner'which does place n oreiithan one signal on a. channel by superimposnot approach the square wave pu'ls'e desired for .jgating purposesl The addition of thetwo pulses'in accordance with one aspect of my invention more nearly. approaches the-desired: squareiwave pulsejshape. By the addition of morepaths other wave. shape characteristicscan be achieved.

A typical set. of valuesifor the embodimentof Fig. 1 employ'edin one application of my in'vention is asfollowsz-the "core" 10 is Ar"thickthroughout; the upper and lower portions of the core10 are% in width; outside legs "ILa'nd IZ .are /3" wide and h,igh;. inside leg 1 3 is A6" wide and' "'hi'gh, Legs 11, 12,.,13 have air gaps 14, 15, and 16 respectively, ofthe order of 0.001. The.insidegfdistancebetween. ;the,legs '11 and 12 is W and between,the.legs. 12,.and:13,1%" and thus the overall length of the l0wer,; a nd upperbranches is 2",. ,Core. 10-is.composed;,of,ferrite material having-a substantially. rectangular 1 hysteresis loop with characteristicssimilai: to iiGeneral Ceramic S1,.:. .1.1at1';ial ,or'other comparable material. As, an,al-te rnativ,e,1 magnetic metals exhibiting approximatelyrectangular; hysteresis loops can be used; if; the :core. structure is laminated. The respective windingschave .the following. turns and wire "sizes:

Fig. 4 illustrates an alternative core structure employing the addition of more paths as mentioned above. A core 27 has an input leg 28 and three output legs 29, 30 and 31. The input leg 28 has an area at least equal to those'of the combined output legs 29, 30 and 31 in order to allow their complete saturation. The core 27 may also be tapered as shown since the minimum required areas of the upper and lower portions must be greater to the left of leg 29 than of 30, etc., again in order to saturate all output legs. An input winding N is wound on input leg 28 and output windings N N and N are wound on legs 29, 30 and 31 respectively. Winding N: has terminals 32 and 33, winding N has terminals 34 and 35 and winding N has terminals 36 and 37. Input winding N has terminals 38 and 39.

An input signal applied to terminals 38 and 39 in the proper polarity to reverse the saturation of the presaturated output legs 29, 30 and 31 first drives leg 29 through the unsaturated region, then leg 30 and lastly leg 31. During the excursion through the unsaturated region of these legs, sequential'output pulses are generated in windings N N and N These pulses may be added in series by connecting together terminals 33 and 34 and also connecting together terminals 35 and 36. If it is desired to use the pulses separately, terminals 32, 34and 36 may be connected to provide a common terminal and sequential outputs taken from terminals 33, 35 and 37.

By modifying the input voltage to winding N1 the time of the initial outputpulse across winding N may be varied. For instance, a square wave of large magnitude generates an output pulse across N substantially simultaneously with its application. By proper design of the parameters the output pulses can be made to either directly follow one another or to be spaced in time from each other. Application of electrical biases to the legs 29, 30 and 31 can also be utilized to position the respective output pulses in time as desired.

As illustrated in Fig. 4 the core 27 has no air gaps. This may be advantageous if it is desired to obtain a series of short pulses which need not meet critical width requirements, because an air gap tends to cause the hysteresis loop to take more of the shape illustrated in Fig. 3c with the S-shaped portions which hinder sharp leading and trailing edge resolution.

The alternative embodiment of Fig. 5 employs two toroidal cores 40 and 41, the core 40 having air gaps 42 and 43 and the co e 41 having no air gap. An input winding N is wound on core 40 and an input winding N is wound on core 41. Windings N and N are connected in series aiding to signal generator 18 across terminal 17 with a resistor 44 shunted across winding N An output winding N is wound on core 40 and an output winding N is wound on core 41. These output windings N and N may be connected as illustrated in series aiding to output terminals 19 and 22 to secure composite output pulses by connecting terminals 20 and 21, or alternatively, individual output voltages may be obtained by separate connections to free terminals 19 and 20 and common terminal 20 or 21 in a manner herein before explained. In the embodiment of Fig. 5 the delay between the two magnetic paths can be varied in three ways. In the core 40 air gaps 42 and 43 can be employed to tilt the hysteresis loop in a manner illustrated in Fig. 3b for the purpose of reducing H and the resulting delay due to the core 40. On the other hand, the delay produced by core 41 can be increased by reducing the number of turns on the signal winding N and by shunting a portion of the signal current to the winding N through resistor 44. If required for any particular application, the number of turns on the output windings N and N can be adjusted to give voltages of equal magnitudes when the respective cores 40 and 41 are out of saturation.

I have described one specific embodiment of my invention to be employed as a delay element in a color television receiver. However, it will be apparent from the discussion of the other embodiments that the delay element embodying my invention has several possible applications, such as in the pulse communication systems, radar range gates, and digital circuitry applications mentioned. Thus, while I have shown particular embodiments of my invention, it will be understood, of course, that I do not wish to be limited thereto since many modifications may be made and I, therefore, contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electrical signal delay device comprising a plurality of magnetic circuits, input winding means inductively coupled to said magnetic circuits, means for supplying said input winding means with an input signal of reversible polarity having suflicient magnitude to saturate at least a portion of each of said magnetic circuits first in one direction and then in the opposite direction, each of said circuits having a combined reluctance and ampere-turn energization different from the remaining circuits whereby each circuit unsaturates and saturates respectively at different times from the remaining circuitsduring application of said signal, and output winding means coupled to each of said magnetic circuits for deriving a reversible output signal during the times said circuits are in their respective unsaturated conditions.

2. An electrical signal delay device comprising a plurality of magnetic circuits, input winding means inductively coupled to said magnetic circuits, means for supplying said input winding means with an input signal of sufficient magnitude and of proper polarity to saturate at least a portion of each of said magnetic circuits first in one direction and then in the opposite direction, each of said circuits having a combined reluctance and ampere-turn energization ditferent from the remaining circuits whereby each circuit unsaturates and saturates respectively at different times from the remaining circuits during application of said signal, and output winding means respectively coupled to the portion of each of said magnetic circuits which saturates and unsaturates during application of said signal.

. 3. An electrical signal delay device comprising a plurality of magnetic circuits, input winding means inductively coupled to said magnetic circuits, means for supplying said input winding means with an input signal of sutficient magnitude and of proper polarity to saturate at least a portion of each of said magnetic circuits first in onedirection and then in the opposite direction, each of said circuits having a combined reluctance and ampere-turn energization different from the remaining circuits whereby each circuit unsaturates and saturates respectively at different times from the remaining circuits during application of said signal, and output winding means respectively coupled to the portion of each of said magnetic circuits which saturates and unsaturates during application of said signal, said output winding means each having at least two terminals from which a pulse may be taken while the magnetic circuit to which such output winding means is coupled is driven from saturation in said one direction to saturation in said opposite direction.

4. The device of claim 3 in which said input signal is a reversible square wave voltage having negligible rise time in order to initiate an output substantially simultaneously with the application of said input signal.

5. An electrical signal delay device comprising a plurality of magnetic circuits, input Winding means inductively coupled to said magnetic circuits, means for supplying said input winding means with alternating current of sufiicient magnitude to cause saturation of at least a portion of each of said magnetic circuits, each of said amass; V

circuits having a combined reluctance and ampereturn energizationx'dilferent from the remaining circuits whereby each circuit saturates and unsaturates at different times fromtheremaining'circuits during each cycle of input alternating current, and output -winding means coupl-edto each of said magnetic circuits for'deriving a composite rectangular output voltage pulse representing the addition of the voltage pulses which are time-sequentially induced in the output winding means aseach magnetic circuit passes through an unsaturated region.

-6. -An'electrical signal delay device comprising a plurality-of-magnetic circuits, input winding means inductively coupled to said magnetic circuits, means for supplying'said input'wi nding means with a saw toothalternating current of sufficient magnitude'to cause satura tion of at least a portion of all said magnetic circuits,

7 each of said circuits having a combined reluctance and ampere-turn energi'zation different from the remaining circuits Wherebyeach circuit saturates and unsaturates at different'times from the remaining circuits during each cycle of input alternating current, and output winding means coupled to each of said magnetic circuits, each of said output winding means having two terminals, said terminals connecting said output winding means in series aiding for deriving-a composite rectangular output voltage pulserepresenting the addition of the-voltage pulses whichare-time-sequentiallyinducedin the output winding means as each magnetic circuit passes through an unsaturated region. e

7. An electrical signal delay device comprising a three-legged-magnetic corehaving an inside leg shifted off center defining two magnetic paths of dilferent lengths, input winding means inductively coupled to said core, a saw tooth current input signal generator connected-to said inputwinding' means, the signal fromsaid generator having a magnitude sufficient to saturate at least a portion'of said paths alternately in both directions and suflicient 'to drive saidpaths individually out of saturation after the change in polarity of said signal at diiferent preselected times determined by their -magnetic field intensities, output winding means inductively coupled to said core in order toobtain a continuous substantially rectangular output pulse composed of the addition of the voltages transformed across the separate paths dur ing the time each path is passing through the unsaturated reg on, one of said winding means being wound, on said inside leg and the other including two separate windings connected in series-aiding each wound on a different one of said oaths external to said inside leg.

8. The device of claim 7 inwhich each ofsaid legs has an airgap therein. I

9. A burst gate 'delaycircuit for color television receivers comprising a-three-legged rectangular magnetic core having an inside leg shifted off center defining two magnetic paths of diiferent lengths, said inside leg havinga greater cross section than either of the remaining legs, an input winding on said insideleg, a saw tooth current input signal generator connected to said input winding, the signal from said generator having a magnitude sufiicient to saturate at least a portion of said paths alternately in both directions and sufiicient to drive said paths individually out 'ofsaturation after the change in polarity of said signal at different preselected times determined by their magnetic'field intensitie's,, a separate output winding on-the portion ofeach of said magnetic paths external to said inside leg, said output windings being connected in series aiding, whereby a substantially rectangular output pulse appears across said series outputs'windings composed of the addition of the voltages transformed across the paths when they pass through the unsaturated region, said output pulse being timed to coincide with the time of the color burst on a received television signal and being used to gate a] color burst amplifier.

10. The circuit-of claim 9 in whicheach-ofsaid'three legs has an air gap of substantially equal magnitude therein.

11. An electrical signal delay device comprising a saturable magnetic core having a substantiallyrectangm lar hysteresis loop, said corehaving at'least three apertures linearly disposed therein to create a plurality of magnetic circuits each including an upper and a lower core section and an interconnectingleg, a cross section of one of said legs being at leastequal to the sum of the cross sections of the remaining legs, said upper'and lower 'core sections having cross sections at any position thereon at least equal to the sum of the crosssections of all the legs disposed on the side'of said position rerr otegtrom said one leg in order toallow passage of sufiicient flux to saturate all of said legs, an input winding wound on said one leg, an AC. input signal generator connected to said input winding, the signal from said generator having a magnitude sufiicient to saturate at least a portion of said remaining legs alternately in both directionsand to drive them out of saturation after a change "in polarity of said signal at preselected times depending on their magnetic field intensities, a separate output winding wound 'on each of said remaining legs, and a pair of terminals on each of said output windings for obtaining individual output pulses therefrom duringeach cycle of said input signal.

12. An electrical signal delay device comprising a plurality of magnetic circuits, input winding means inductively coupled to said magnetic circuits, means for supplying said input winding means with an input signal of reversible polarity having sufiicient magnitude to saturate atleast a portion of each of said magnetic circuits first in one direction and then in the opposite direction,at least one of'saidcircuits'having a combined reluctance and ampere-turn-energization different from the remaining circuits whereby said at least one circuit unsaturates and saturates at-a difierent time from the remaining circuits during application of said signal, and output winding means coupled to each of said magnetic circuits for deriving an output signal during the times said circuits are in their unsaturated conditions.

References Cited in the'file of this patent UNITED STATES PATENTS 

